Remove custom SkVertices data and runtime effect `varying` support

This was an experimental feature. It worked (but only the GPU backend).
It was never adopted or used by anyone, to my knowledge. It's a large
amount of code, and a strange corner of SkSL for users to stumble into.

Bug: skia:10680
Change-Id: I0dda0364bce7dbffa58c32de4c7801ec2a6bc42e
Reviewed-by: Mike Reed <>
Commit-Queue: Brian Osman <>
28 files changed